1. Field of the Invention
The field of the invention is backpack-type sprayers for spraying liquid under pressure.
2. Prior Art
Various United States patents have been obtained for hand-operated backpack-type sprayer combinations adapted to spray liquid chemicals such as insecticides, fertilizers, fungicides, etc. These include U.S. Pat. Nos. 4,690,331; 4,702,416; 4,702,419; 4,768,714; 4,798,333; and 5,335,853, each of which is incorporated herein by reference. The constructions shown and described in the specified patents, with the exception of U.S. Pat. No. 5,335,853, include relatively large-diameter diaphragms that are used to pump liquid from a storage tank to a pressurized container. The diaphragms are often combined with a piston such that the diaphragm-piston combination not only pumps and pressurizes the liquid, but also agitates and mixes the liquid in the bottom of the storage tank.
An important consideration for portable sprayers is leak prevention. As indicated above, the sprayers are frequently used to spray insecticides, fungicides, and fertilizers, all three of which may be hazardous to either the operator or the surroundings if not properly protected. Diaphragms are very good at sealing against leakage. However, after prolonged use in association with certain types of chemicals, even the best diaphragms may eventually fail. Upon occurrence of diaphragm failure, the chemicals within the sprayer tend to leak out the bottom of the structure and may come into contact with the operator or the surroundings.
The invention claimed in U.S. Pat. No. 5,335,853 replaces the diaphragm with a piston assembly in order to help reduce leakage. However, leakage may still occur through the piston assembly if portions of that assembly fail to operate as intended due to extended use or wear and tear. Regular preventive maintenance becomes necessary to replace parts of the sprayer before a failure, and the associated leakage, can occur. A sprayer capable of protecting against leakage when such failure occurs is therefore desirable.
In accordance with the present invention, a compact, strong, long-lasting portable sprayer having a piston assembly which protects against leakage is disclosed. The piston has a double-walled construction, which in conjunction with the piston cylinder define a primary leak collection chamber. Liquid leaking from the piston assembly is collected in the primary chamber and expelled into a secondary leak collection chamber by the reciprocating action of the piston. The secondary collection chamber is defined by affixing a leak barrier, preferably an expandable bellows, to both the piston and the pressure vessel. Once in the secondary chamber, liquid may be pumped into the tank through a siphon by the reciprocating action of the piston. In returning the liquid to the storage tank, the siphon disperses liquid in an upper interior portion of the tank so that the reciprocating action does not pump liquid from the tank through the siphon.
In an alternative embodiment, a one-way valve may be placed on the siphon so that liquid may not be pumped from the tank through the siphon.